1. Field of the Invention
The present invention relates to an animal cell growth-promoting agent and to a serum-free culture medium which contains the animal cell growth-promoting agent.
2. Description of the Prior Art
Conventionally, 5 to 20% of serum is usually added to a liquid culture medium for animal cells, in addition to amino acids, vitamins, sugars and inorganic salts. If the serum is removed, the cells stop growing and die off.
However, the use of the serum has several disadvantages; namely 1) the serum is so expensive as to amount to 75 to 95% of the total cost of the medium, 2) the serum is extremely different from one lot to another so that stable cell growth can not be attained, 3) the serum can not be sterilized by autoclaving so that contamination by mycoplasmas or viruses may occur, 4) the serum contains more than 500 kinds of proteins so that isolation and purification of physiologically active substances produced by cells are difficult. Consequently, serum-free culture media are used in order to solve these problems.
A number of serum-free culture media are known, i.e. a serum-free culture medium which contains Eagle's MEM (Minimum Essential Medium) as a basal culture medium and additional supplements such as albumin, insulin and transferrin and a serum-free culture medium which contains a modified Eagle's MEM as a basal culture medium supplemented with a cell growth factor obtained by fractionation of bovine serum using ammonium sulfate.
The above-mentioned serum-free culture media have been widely used for cultivation of animal cells. However, also they have problems; namely 1) their cell growth-promoting effect is less as compared to culture media containing serum, 2) serum components are substantially used although they are fractionated and 3) they are costly and not necessarily economical.